1. Field of the Invention
The present invention relates to an electronic timepiece that performs near field communication with an external device.
2. Description of Related Art
With the development of low-power technique for the near field communication using Bluetooth®, for example, there has been a technique in which an electronic timepiece and a cellular phone, such as a smart phone, as an external device are connected and communicate with each other almost constantly to perform various communications with each other. For example, the smart phone can transmit time data to the electronic timepiece. As another example, the smart phone can send information of arrival of an e-mail or a call to the electronic timepiece, and a ringer tone or message alert tone and/or vibration of the smart phone can be stopped upon a user operation of the electronic timepiece when the smart phone is ringing.
In the case of an electronic timepiece that is almost-constantly connected with a cellular phone such as a smart phone using the near field communication technology, it is desired that a built-in button primary battery last for a few years as in the case of general wristwatches. When the electronic timepiece is almost-constantly connected with a smart phone with the Bluetooth®, for example, the battery life is profoundly affected by an operating current of a Bluetooth® module which performs transmission and reception. Accordingly, in order to keep the almost-constant connection for a user while extending the battery life, it is required that the power of the Bluetooth® module be frequently turned on and off to reduce accumulated power-on time of the Bluetooth® module as much as possible.
Japanese Unexamined Patent Application Publication No. 2007-178303 discloses an electronic pedometer having an acceleration sensor and a tilt sensor. In this electronic pedometer, when the tilt sensor determines that the pedometer is inclining, the acceleration sensor counts the number of steps.
A user who wears an electronic timepiece, however, makes various movements other than walking and running. When the electronic timepiece is almost at rest, e.g., when the user crosses his or her arms in a meeting or on the train, or when the user is driving on an express highway, for example, the movement of the electronic timepiece cannot be fully detected. As a result, the power of the Bluetooth® module is turned off in such situations, which causes the following problems.
In the past, an electronic timepiece has been used mainly for a clock function. The electronic timepiece, therefore, has been checked only when a user needs to know the time. Accordingly, in the case of a conventional timepiece, when the user needs to know the time, the user has only to cancel the time-display-off mode by moving his or her arm, for example, to display the time again. A constantly-connected timepiece, however, cannot receive information of incoming phone calls or e-mails from the smart phone when the power of the Bluetooth® module is off. Even if a user turns on the power by moving his or her arm later, the information of incoming phone calls or e-mails during the power-off period cannot be received. Therefore, in the case where the electronic timepiece is almost-constantly connected with the smart phone with the Bluetooth®, a more precise movement-detection technology and a better power-saving technology are required.